However, some of his own MPs, including former prime ministers Boris Johnson and Liz Truss, have voiced opposition to the legislation, as well as the DUP.
But the Government is understood to be confident that it has the support to get the fresh Brexit deal over the line with or without the support of rebels, with the number of MPs expected to voice their opposition to the plans thought to be as low as 20.
What is the Windsor Framework?
Mr Sunak unveiled his new Windsor Framework last month, which is designed to fix problems with the Northern Ireland Protocol.
The Northern Ireland Protocol ensured there remained an open border between Northern Ireland and the Republic of Ireland after Brexit.
However, it came at the cost of a regulatory border being set up between Great Britain and Northern Ireland, which meant inspections on some goods – such as meat, milk, fish and eggs – from England, Scotland and Wales had to take place at Northern Irish ports. This complicated trade between Northern Ireland and Great Britain, with critics arguing it weakened its place in the UK.
Under the new legislation, which was co-signed by the Prime Minister and Ursula von der Leyen, the President of the European Commission, some EU-imposed checks on goods heading west over the Irish Sea will be eradicated.
Mr Sunak promised that all items available in British supermarkets will also be sold in Northern Ireland, while medicines approved by the UK’s regulator will no longer be held back from the Northern Irish market.
Should it get through Parliament it will still take several years for the new deal to take full effect, with businesses given months to adjust to the updated regulations.
Speaking in Windsor, the Prime Minister said: “Today’s agreement delivers smooth-flowing trade within the whole United Kingdom, protects Northern Ireland’s place in our union and safeguards sovereignty for the people of Northern Ireland.”
Ms von der Leyen added: “This new framework will allow us to begin a new chapter. It provides for long-lasting solutions that both of us are confident will work for all people and businesses in Northern Ireland.”
As part of the deal, the EU will still have some power over Northern Ireland. EU law will still apply to some industries, particularly on food and animal products, and the European Court of Justice will remain the arbiter of how it operates.
However, the Prime Minister secured the so-called “Stormont Brake”, which will allow the Northern Ireland Assembly a veto to stop any new EU legislation applying in the region.
This comes with strings attached, including tough conditions for its use and the possibility of the EU retaliating by suspending single market access.
The Brake will allow 30 MLAs from two or more parties in the Stormont Assembly to object and effectively suspend a potential rule change from coming into effect.
It can only then be applied if the UK and EU agree jointly, essentially giving Westminster a veto over new EU laws applying in Northern Ireland.
The Brake should be used only as a last resort if MLAs can show the EU law in question would have a “significant impact specific to everyday life”.
A No 10 spokesman said that “the Prime Minister thinks this is the best deal that is available to Northern Ireland.
“This is something that the Government has been working on for a long time. It fixes the problems that we know existed in the protocol and the impact it was having on people’s everyday lives in Northern Ireland.
“We think this is the right deal”.
What time are MPs voting?
The vote on the deal should get underway around 2.30 pm – shortly after Mr Johnson will face questions from the Privileges Committee about whether he intentionally misled Parliament over lockdown parties.
The vote is on a key part of the deal, the Stormont brake, designed to give a Northern Ireland Assembly a say on how EU laws apply there.
Under the brake, Northern Ireland assembly members could object or raise concerns to some of changes to EU laws, potentially leading to suspension of the law.
The Stormont has not been sitting since February last year, when the DUP resigned from the first minister role in protest against the Northern Ireland Protocol.
The DUP have said eight MPs will vote against the Stormont brake and other Tory MPs may do so also.
DUP leader Sir Jeffrey Donaldson has made it clear that the party would oppose the Windsor Framework in the Commons on Wednesday, while demanding “clarification, change and reworking”.
Which MPs could rebel?
Former Prime Minister Boris Johnson has said he will vote against the deal, while another former Prime Minister Liz Truss is understood to also be voting against it.
In a statement Mr Johnson said: “The proposed arrangements would mean either that Northern Ireland remained captured by the EU legal order – and was increasingly divergent from the rest of the UK – or they would mean that the whole of the UK was unable properly to diverge and take advantage of Brexit.”
Shortly after his statement, Ms Truss also confirmed she is set to vote against the deal. She believes that the Windsor Framework does not “satisfactorily resolve the issues thrown up by the Northern Ireland Protocol”.
“That is not acceptable. I will be voting against the proposed arrangements today. Instead, the best course of action is to proceed with the Northern Ireland Protocol Bill, and make sure that we take back control,” Ms Truss said.
Priti Patel has also joined the rebellion, with the former Home Secretary telling The Telegraph she would “not be buying shares on the Government’s smoke and mirrors on Windsor”.
Former Conservative Party leader Sir Ian Duncan Smith has also announced he will not be supporting the deal.
There is speculation the European Research Group (ERG) of pro-Brexit Tory MPs could also vote against Mr Sunak’s Windsor deal.
ERG chairman Mark Francois MP described the Stormont brake as “practically useless”, that the overall agreement would leave EU law supreme, and that the “framework itself has no exit”.
But he did not confirm that members of the group would vote against the deal, and a senior source told i the ERG group would not vote as a block against the deal.
Former Conservative Party leader Sir Ian Duncan Smith also told The Telegraph he would not be supporting the deal.
The DUP has already said its eight MPs will vote against the regulation to implement the so-called Stormont brake, which would allow the Northern Ireland to reject EU rules that apply in the province, as it continues to seek changes to the overall framework.